Electric precipitator tube cleaning method



Fell 14, 1950 J. B. JONES El Al.

ELECTRIC PRECIPITATOR TUBE CLEANING METHOD 2 Sheets-sheet 1 Filed Nov. 27, 1944 F 1950 J. B. JONES ETAL 2,497,171

ELECTRIC PRECIPITATOR TUBE CLEANING METHOD Filed Nov. 27, 1944 2 Sheets-Sheet 2 T 7 i J INVENTORS JOSHUA BJONES and Patented Feb. i4, 1950 THOD Joshua B. Jones and Richard H. White, Youngstown, Ohio, assignors to Carnegie-Illinois Steel Corporatioma corporation of New Jersey Application November 27, 1944, Serial No. 565,298

1 Claim.

This invention relates to a method of cleaning tubes. More particularly the invention relates to a method for removing deposits, such as mud and scale, from the inner surfaces of tubes.

The invention has as one object thereof the provision of a simple, fast, and economical method for removing. deposits, such as mud and scale; from the inner'walls of tubes.

Another object of the invention is the provision of a simple, easily operated, device for use in practicing the cleaning method of the invention.

These and iurther objects will become ap parent in the following description.

' The method of the present invention is particularly useful in the cleaning of electric precipitator'tubes upon which particles are deposited from the gas passing therethrough by being ionized by the high tension electric iield set up between the tube, as one electrode, and a wire passing through the tube coaxially thereof, as the other electrode. Precipitators of such type are commonly used in the metallurgical field, for instance, to remove dust from the exhaust gas of a metallurgical blast furnace. In some electric precipitators, a thin film of water traveling downwardly is maintained on the inner walls of the precipitator tubes and the precipitated particles are caught in such him and carried downwardly into a sump. Because of the slow rate of travel of the film of water, it fails'to remove all of the dust particles from the inner surface of the tube and a layer of mud and/ or scale gradually builds up on the inner surface of the precipitator tube to such a d'epth'as to-interfere with the operation of the device. It is with the removal of such layer that the method. of the present invention is particularly concerned, although it is to be understood that the invention finds utility in the cleaning of the inner surfaces of various other tubes having slmil'ar'deposits therein.

The invention will be more readily understood by reference to the accompanying drawings, in which:

Figure 1 is a view-in side elevation of an electric preclpitator, portions of the shell of the precipitator being broken: away for clarity;

Figure 2 is a schematic view of a precipitator tube and its central electrode, as used in the apparatus of Figure 1;

Figure 3 isa view similar to Figure 2, but showing. the tubecleaning device of the present invention inserted. into the tube for cleaning'the latter;

Figure 4 is an enlarged view of the cleaning de- 2 vice shown in operative relation to the section of the tube being cleaned; and

Figure 5 is a view in section taken along the line of V--V of Figure 4.

The electric precipitator shown in Figure 1, consists of an upright, generally cylindrical, structure having side walls 2 and bottom 4 and top 6 joined thereto to form a gas-tight structure. At approximateliy one-quarter of the distance from the top end of the enclosure, there is positioned a horizontal bulkhead t separating the top of the shell from the bottom except through the openings provided by the precipitator tubes, subsequently to be described. Access to the portion of the shell above the bulkhead is gained through door 9, which is made large enough to admit a man for the purpose of mounting or adjusting the electrodes and for cleaning the tubes.

The preclpitator tubes l0 hang through holes in bulkhead 8, and are suspended therefrom by their flared upper ends ii. In order to cause the gas travelling through the precipitator to be subjected to a high tension field, each of the tubes it, of which there may be as many as 100, 125.

or more, is provided with a coaxial electrode it in the form of a twisted cable held by the top electrode holder i6 insulated from the frame of the precipitator and the bottom electrode holder 88, likewise insulated from the frame. The elec trodes M are supplied with high tension current by means of high tension line 20 connected to a suitable source (not shown). The other side of the high tension line is connected to the ground, as is the frame of the precipitator, and thus each of 'the precipitator tubes is at ground potential.

Gas to be cleaned in the precipitator enters from each side of the shell through the inlets 22, whence it travels in the direction indicated by the dotted lines in Figure 1 down into the bottom ends of the precipitator tubes ill. The gas then travels upwardly through the tubes,

where it is subjected to the high tension field, I

and, after leaving the upper ends of the tubes It, the cleaned gas flows to one or more gas outlets 24' at the upper end of the shell, as indicated by the dotted lines in Figure 1, and from theoutlet or outlets it is led into ducts for further utilization. A thin film of water traveling in adownwardly direction is maintained on the inner surface of each of the precipitator tubes by virtue of the overflow into them of the water layer 26 on the bulkhead 8. Such downwardly traveling film of water is designated 28 in Figure 2; The layer of mud or scale formed on the inner surface of the tube, shown in Figure 2 and designated 30,

- film flows rather than the desired smooth surface of the tube, thereby encouraging still further depositions of mud, scale, and the like. It is, therefore, necessary to clean the precipitator tubes of the device, such as shown in Figure 1, at

regular intervals to maintain the efficiency of the precipitator as high as possible.

While the tubes are being cleaned, it is necessary to remove the precipitator from the gas source and to disconnect the central electrodes from the source of high tension current. The precipitator tubes were formerly cleaned, after such steps were taken, by two men, one above the upper end of the tubes and one below the lower end in the precipitator shell. The workmen loosened and removed the central electrode in each tube, inserted a long handled brush in the tube, and pulled and pushed on such brush alternately to propel it back and forth in the tube. Following such brushing, the tube was flushed with a stream of water, and then the central electrode was replaced. The total cleaning time for a precipitator employing 114 tubes was approximately nineteen man hours, which meant that the precipitator was necessarily out of serv-- ice for at least 8 hours, if two men were employed during the cleaning operation.

The method and apparatus of the present invention materially shorten the time which the precipitator must be out of service, even though only one man is employed for the cleaning operation as compared with the two used formerly. The cleaning apparatus of the present invention, shown in Figures 3, 4, and 5, consists of a jet device or jet head 32 chambered, as shown in Figure 4, to provide a hollow interior 34. The jet head is made in the form of a disk having a radius slightly smaller than that of the bore of the tube to be cleaned. Such difference in radii may be, for example, on the order of V; of an inch. In general, the tubes are cleaned in accordance with the present invention before layer 30 has reached such thickness that jet head 32 may not be slid freely through the uncleaned tube. The periphery of the disk is provided with a plurality of at least substantially radially directed bores 38 communicating with the hollow interior, such bores acting as jets. The jet head is supplied with a compressed gas, such as compressed air, through flexible hose 42, the end of which is provided with valve ll and is connected with the jet head by means of pipe 38 screwed into the threaded boss 31 on the top of the jet body. In order to allow the jet to be received within the tube to be cleaned without the necessity of disconnecting the central electrode [4, the jet head is provided with a slot 44 extending at least approximately in a radial direction past the center of the body in an amount suflicient to allow reception of the electrode therein and travel of the jet head relative thereto without contact between them. It has been found that the layer of mud and/ or scale on a precipitated tube is sumciently disrupted and loosened to allow its ready removal by flushing with a stream of water by use of the jet head of the present invention when an air pressure in the jet head of from 90 to 100 pounds per square inch is employed and inch diameter holes or jets spaced inch center to center around the periphery of the jet body are 5 employed.

After its introduction into the tube to be cleaned, the jet body is slowly lowered down the tube suspended from hose 42, until it has traversed the full length of the tube. Such lowering is carried on slowly enough to insure thorough loosening of the deposit in each zone of the tube. To insure the loosening of the deposit at a point opposite the opening of the slot 44 the hose pipe 42, by which the jet body is suspended, may be oscillated slightly to cause the jet head to swing sufficiently to allow the jets 36 to cover the portion of the wall opposite such slot. After all the inner surface of the tube has been subjected to the action of the jet head, the jet head is retracted from the tube and the loosened mud or scale is removed by a high pressure stream of water, which may be applied from a hose directed into the tube from above.

The use of the jet in the present invention followed by fiushing with water results in the removal of mud and/or scale layer 30 in a more thorough manner than is possible with brushing and subsequent flushing. In addition, the cleaning is carried out at a much more rapid rate than was possible with the brush cleaning heretofore used, partly because there is no necessity for disassembling the central electrode and partly because the action of the compressed air jets in striking the inner surface of the tube in at least a substantially radial direction and from a point spaced very close to such wall results in a loosen ing of the dirt layer in a much faster, more thorough and efficient manner than is possible with brushing. This is true because the air jets have suflicient force to penetrate the layer of mud and/or scale to the tube wall. At least part of the compressed air reaching the tube wall then flows laterally, effecting loosening and removal of the deposit from portions of the tube wall in the region of any particular jet but not directly in line with it. The action of the brush, on the other hand, is inherently limited to the surface of the deposit, which must be removed by the brush layer by layer until the tube wall is finally reached. As a result, by the use of the present apparatus the 114 tubes of the precipitator shown may be completely cleaned in five hours by one man, which amounts to a little more than onequarter the man-hours formerly required in the 55 practice of the former method of cleaning.

Although a particular embodiment of the apparatus has been shown and described for purposes of illustration, and the method and apparatus of the invention have been disclosed in con- 60 nection with the cleaning of tubes in a particular kind of apparatus, it is to be understood that the invention is not to be limited thereto, but that its scope is defined in the appended claim] We claim:

The method of removing adhering deposits of mud or scale from the inner surface of an electric precipitator tube having an axially directed electrode therein, which comprises inserting in the tube a disc shaped air jet device having a 70 radius slightly less than that of the bore of the tube, and having a slot therein to receive the electrode, said jet device being provided with a plurality of substantially radially directed jets on its peripheral surface, subjecting the inner wall 75 of the tube to jets of compressed air'from the Jet device. movin: the Jet device axially of the. Number mi new tube to subieot at least substantially all the inner 022,863 Stuart May 18, 1909 surface of the tube to the compressed air Jets, 1,082,974 Ssrzeent Apr. 9, 1912 whereby to loosen the deposits from the tube. 1,161,467 Gallup Nov. 28, 1915 withdrawing the Jet device from the tube, and 1- 1,798.87! Watson Mar. 1'1. 1931 flushing the loosened deposit from the tube by s 2, 4 ,752 But worth n 3 19 6 stream of water. 2,179,473 HcDevitt Nov. 7; 1989 JOSHUA B. JOIFES. 3,374,399 Weir Apr. 24, 1945 RICHARD m roman rs'mm's REFERENCES CITED Number Country Date The following references are of record in the Austral 1929 file of this pltent: UTHERREFERENCES UNITED STATES PATENTS 1 Fisher, "Modern Laboratory Appliances," page 78. Fisher Scientific 00.. Pittsburgh, Pa" copy- Number Nome Dote $048,198v M No a n rishted 1934. (EDDY in Division 59.) 

